As transfer sheets used in printing methods of this kind, there have heretofore been used those which are made of polyester fiber excellent in stability and contain a dye for transfer and textile printing, but since the sublimation property of the dye contained is insufficient, the transfer sheets of this kind are poor in tinting strength, so that it has been difficult to attain a sufficient depth of color by means of heat energy supplied from a conventional thermal head.
Although ion-type dyes containing a color former rich in sublimation property can give a sufficient depth of color, the storage stability of a printed image on the printing sheet obtained by using these dyes have been insufficient.
On the other hand, the printed image produced by these dyes has a disadvantage of unevenness of its quality particularly in the region of intermediate color tone, and the main causes of this disadvantage have been dropout of printing in portions to which energy is applied and sublimation or spattering (noise) of the dye in portions to which no energy is applied.
Further, particularly when a thermal head is used as a means of printing, substrates for transfer sheet made of an inexpensive and homogeneous film which are used for obtaining a homogeneous image is, in some cases, fused together with the thermal head by an intense heat generated by the thermal head, so that their stable running on the thermal head has been difficult.
On the other hand, as an image-receiving sheet in which an image is formed by selectively heating a dye on the transfer sheet according to signals of the image, there is used one which comprises paper made from pulse and having an uneven thickness as a substrate for image-receiving sheet and a development layer formed thereon which is composed of inorganic fine particles and a binder having dye-affinity such as polyester. Therefore, the printed image obtained has no smooth quality in the region of intermediate color tone, and no image having a high printing density can be obtained. Moreover, the printed image obtained is poor in stabilith, for example, light resistance.